Recent advances in surface science, such as the invention of the Scanning Tunneling Microscope with which surface features down to the atomic level can be resolved, and in manufacturing where surface structures below 1 .mu.m are within reach of device manufacturers, have created a great desire for positioning devices which permit the displacement of objects or tools, like electrodes, over millimeters or even centimeters, but with a reproducible accuracy in the range of nanometers. In addition to positioners which permit linear displacements, there exists a strong requirement for rotary positioners.
In view of the fact that essentially all investigations of surface features and manufacturing steps that involve structures of the size indicated above require the absolute avoidance of contamination by dust and humidity, the positioners used in these applications must be vacuum-compatible and be able to resist baking up to about 500 K. Also, to be able to resolve features down to the atomic level, the positioners used must be free of vibrations to a very high degree, i.e. they have to be mechanically decoupled from the outside world. These requirements can be met by positioners working with piezoelectric elements which are controlled by electrical potentials applied to their electrodes.
Known in the art are piezoelectric positioners which permit longitudinal translation of an object, such as the one shown by Binnig and Gerber in IBM Technical Disclosure Bulletin, Vol. 22, No. 7, p. 2897 where a H-shaped piezoelectric member can move in a trough-like channel by alternatively clamping pairs of legs against the channel walls and contracting and expanding its center portion. Of course, the Binnig, et al straight channel permits only linear motion.
Also known in the art is another class of piezolectric positioners which avoid the channel in favor of greater flexibility of movement. They use a tablelike configuration, as shown by Binnig and Gerber in IBM Technical Disclosure Bulletin, Vol. 23, No. 7B, p. 3369, where the table rests on eight piezolectric legs, four of which are connected to an inner section of the table, the others to its outer section, the sections being linked by piezolectric elements. By controlled lifting and lowering the said groups of legs and through appropriate extension and contraction of the linking elements, the table can be moved in orthogonal directions.
Another table configuration is known from U.S. Pat. No. 4,422,002, issued to Binnig, et al, where the piezolectric table has three legs whose bottom surfaces are equipped with electrostatic clamping means which permit selective clamping of the legs to a bench. Appropriate control of the actuating voltages at the table and the legs causes the device to move linearly or pivotally about its legs.
Obviously, only the last-mentioned positioner permits some rotary motion, but because of the threeleg configuration its rotation is not strictly circular so that the re-finding of a once held position is extremely difficult.
Still another type of stepping motor is disclosed in IBM Technical Disclosure Bulletin, Vol. 16, No. 6, p. 1899. Here the periphery of a capstan is engaged radially by a piezoelectrically driven rod which in turn is movable tangentially be a piezoelectric transducer. This motor permits the capstan to perform small rotary steps, suitable for a tape drive as shown, but in no way accurate or reproducible in the sense of scientific or manufacturing applications.